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I had this problem and found the anti-freeze was in pure form. They put in all anti-freeze. You have to put in 1/2 anti-freeze and 1/2 water. With-out water to transfer the Heat, It can not let Heat escape to cool your engine. I put 2 gal's anti-freeze to 2 gal's water. No more over heating...Ken Burchstead
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Ken Burchstead on
8/7/2011 7:46:18 AM
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I am on m,y second 396 and there are several things to look at. It would be good to know a little more history of the problem. What was done recenty t the car? Does this occur while driving or while sitting still? What are you running for coolant?Here are some things to do. How if the clutch fan working? And sop moving it by hand? Does it spin too freely when engine off but after running. you should feel some friction when you spin it. How long has it been on? replace with new or well rebuilt unit. Is all the factory shrouding around the fan. It has to be there or you create a short circuit around the radiator without all insulation. In fact the 67 model with AC has some additional insulation that can help. Never run all water you need a mixture of water and coolant. Check that out. The burping is good. I sometime s run the engine for a while with the radiator cap (surge tank cap) off to make sure all air bubbles get to the top and out of the system. Have you changed the thermostat? They stic at times and need replacement. You can also drill a small hole in the thermstat flange but not where the gasket sits. This allows warm water to get on the back side of the cap which tends to help it sense the temperature.
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Tom Nagle on
2/5/2010 2:23:19 AM
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HI,
I OWNED A NEW 65 396 IN APRIL OF 65. I BLEW IT UP AND WHILE IT WAS AT THE DEALERS GETTING REPAIRED, I GOT TO KNOW THE MECHANIC VERY WELL. WHEN IT WAS PUT BACK TOGETHER, HE TOLD ME THERE WAS A "NOTE TO DEALERS" TO MAKE SURE ANY 396 CORVETTETHAT HAD BEEN DRAINED OF ANTI-FREEZE BE STARTED IN THE FOLLOWING MANNER. THE VEHICLE MUST BE JACKED UP SO THE FILL POINT WAS HIGHER THAN THE REST OF THE VEHICLE. REASON BEING, THE COOLING SYSTEM HAD TO BE BURPED. I HAPPENED TO BE THERE WHEN THIS WAS DONE AND LOW AND BEHOLD THE OVERFLOW TANK DID BURP.
I NEVER HAD A HEATING PROBLEM AND I HAVE RUN INTO SEVERAL PEOPLE IN ALL THESE YEARS THAT DID HAVE A PROBLEM. I RELATED MY ABOVE STORY AND THEY COULD NOT THANK ME ENOUGH. I PRESENTLY HAVE A 65 - 396 VETTE AT THE RESTORATION SHOP AND CLOSE TO START IT UP. I TOLD THE RESTORER THIS STORY AND HE SAID "YES I KNOW THAT"
I KNOW THERE ARE PROBABLY A LOT OF ANSWERS TO YOUR QUESTION, BUT, THIS ONE WORKS.
GOOD LUCK
TIM
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Timothy Bowgren on
2/3/2010 5:33:42 PM
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In view of the fact that C3 and later Corvettes were designed to run at high speed for long periods of time we have to conclude that something is definitely wrong. You've done all the obvious things including checking the timing, but as silly as it seems, is your engine actually at TDC (top dead center) when the harmonic balancer is lined up with the timing mark? We've encountered new and rebuilt balancers that are many degrees off and this is one cause of overheating engines, especially those that take a relatively long time to overheat.
Another cause of overheating in engines that have been rebuilt is exhaust leakage across a head gasket and in certain cases this is very hard to detect. The best way to see if this might be happening is to look at the coolant with the radiator cap off as the engine warms up. If there are consistent bubbles there is probably an exhaust gas leak.
Hot spots in the engine (oxidation deposits in the cooling passages) can cause slow overheating, as can corroded water pump vanes. We'll assume you've checked for these.
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Posted by Administrator on
2/3/2010 3:52:06 PM
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The Water pump could be the problem if it's a rebuilt it could be the problem.
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Posted by Administrator on
2/3/2010 3:51:01 PM
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If your car is overheating when the engine is revved or when driving down the road, the most likely cause that is overlooked is the wound spring that is supposed to be in the lower radiator hose. If it is missing, the LOWER hose will collapse due to the suction effect of the water pump. The faster the pump turns, the more it collapses the hose. If the hoses are not originals, and I'm sure they are not, the spring is probably missing. It usually gets pitched with the old hose. The hoses I've seen from the Corvette suppliers may have all the correct markings, but the spring is usually not there. Try NAPA for a replacement spring.
Other than that, make sure the radiator has the correct seals to the rad support, and the correct seals to the shroud, this is a big deal especially on a big block.
Beyond stock items, Red Line Water Wetter and a Stewart water pump can make a huge difference.
On my 1975 Corvette which ran as hot a many earlier big blocks, when I installed new World Sportsman CI heads, I used all new rad and shroud seals from Dr. Rebuild, changed and checked the calibration of the temp sender, installed a Stewart CI stage I water pump with their replacement t'stat, and retained the stock radiator. Original t'stat was 195, but now I use a 180 and the temp stays at 180. The engine NEVER overheats and actually runs cool during the most severe hot weather (like the 90+ days we've had on the Woodward Dream Cruise).
The heads are a big part of it as the cooling passages are much more generous than the stock castings that restrict coolant flow. Never needed to go to an aluminum rad and I've retained this configuration for over 10 years with no adverse results.
For what it's worth.
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D on
2/2/2010 3:18:06 PM
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I have a 76 with a 506 big block.I stays at 180 to 190.I used a
b cool radiator and electric fans.I had this problem when I first when to a big block.Check the thermostat..Put in in a pot of boiling water see if it opens all the way.Make sure you installed it correct,spring and pellet into the intake.If all is well,get a temperature gun and check the four corners of the radiator.Water might not be flowing evenly.
Is this a new engine.The reason I'm asking is some one might have installed the head gasket in correctly or the wrong ones.
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Henry Callahan on
2/2/2010 2:32:16 PM
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Check your timing.
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Tim Sweet on
2/2/2010 2:12:46 PM
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John,
I have read the others input, and agree on the check list.
I have a `76 350 l-82, and I found it overheated badly too.
All the shrouds and clutch fan and monster radiator are new, as stock! The `76 is a bottom feeded air system and it sucks the hot air right off the road.... almost impossible to cool in the summer!
I checked all you did and the others here but found that the thermostat restricted flow way too much for Florida heat. I gutted the 160* thermostat, popped out the center plunger, and trimmed off two sides of the remaining disc, making a "H plate and this solved all temperature problems and restricted coolant flow perfectly.
Check or replace the clutch fan too!... if all else fails install a rigid fan or flex fan and remove the clutch fan to pull as much air over the radiator as possible! Good luck!
Tom Barth
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Thomas Barth on
2/2/2010 1:29:53 PM
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1: Make sure all the shrouding around the radiator is correct. 2: Make sure your drive belt is not slipping. 3: Double check the vanes on the water pump, just put one on my friends big block, low rpm's OK....High RPM's ran hot. Took the pump off and held the vane and you could turn the shaft. Replaced the pump from another supplier, no problem. 4: Check the pressure on the cap.
Mike S.
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Posted by Administrator on
2/2/2010 10:54:42 AM
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How about the water pump? I had a 67 with the same problem. i changed out everything that I could think of and it turned out to be a bad water pump.
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Leslie Wise on
2/2/2010 10:47:43 AM
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I also have a 65, a 350HP 327 with AC that was overheating under load. That is, it idled OK, but got hot going down the freeway. I spent years going through everything too. I replaced the radiator. Made sure I had the correct water pump. Very important. Some flow too fast, some not fast enough. I had the distributor correctly curved. Checked the timing. Replaced the hoses (make sure you have correct hoses with a spring in the lower). Nothing worked. Finally did two things that worked. First was to get a DeWitts aluminum radiator. I had bought one from LA Radiator with more tubes and fins. In addition to not being correct, it just didn't work well. But at the same time, I also replaced the overflow tank. The mechanic that solved this for me noticed that my old tank, which looked fine, did not seal well, and as a result, the cooling system was not pressurizing. This can be the cause of several issues, including poor water circulation. Very tricky, because when the car is just warming up and you look with the cap off, you see coolant circulating well. But you can't look when it's hot to see that it's not. Those two things worked for me. My car barely gets to 180 now.
Good Luck,
Jeff M.
Newport Beach, CA
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Posted by Administrator on
2/2/2010 10:46:08 AM
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2 things to verify, 1, how well sealed is the shroud area, this forces the air through the radiatior, not around into the engine compartment, and 2 your water pump may be worn out,( impeller ) partially blocked , or slipping ..Vic
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Victor Bellan on
2/2/2010 10:19:55 AM
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Are you sure that it is overheating or are you going by the gauge in the dash? If you are looking at the dash gauge, I would suggest getting an infrared thermometer and checking the engine for the actual temp. You may find that the problem is with the temp sensor at the engine block sending a bad signal to the dash gauge. If you have recently replaced this sensor, I would guess that this is the real problem. Replacement sensors are very frequently inaccurate. If this is the problem, I would suggest contacting Long Island Corvette Supply. They sell a sensor which is calibrated. Hope this helps.
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Don Vaughan on
2/2/2010 9:47:40 AM
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I have a 1971 454 big block which overheated constantly. This wasn't so bad on cooler days and light traffic, but once stalled in traffic or a very warm day it would climb out of site. These vettes are notorious overheaters. I ended up putting in double electic fans, removed the fan from the engine and ran a serpentine belt. Has worked like a charm. NO overheating at all. The engine is an upgrade to 504 HP and can generate a lot of heat. The only thing you might do is recheck to make certain the gauge is reading properly, though. I can assume it is, but might give it a try if you are trying to keep it as original equipment and don't want to do what I did.
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Harry De Butts on
2/2/2010 9:34:32 AM
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